While shooting a 2009 adventure film called “From Time to Time,” actor Hugh Bonneville asked the film’s director, Julian Fellowes, what else he was working on. He mentioned a television miniseries he was writing called “Downton Abbey.” The rest is television history.

A year after the film’s release, Bonneville would come to embody the Earl of Grantham, the stubborn-but-sweet patriarch of a fictitious aristocratic family struggling through war and the sudden decline of Britain as a global superpower. In the show’s fourth season, set in 1922—airing in the U.S. on Jan 5 on Masterpiece on PBS—Bonneville’s character finds himself wracked with grief and trapped between two worlds. Unable to support the family estate, he fights with his daughter, Lady Mary, over whether to sell off land (his idea) or try to turn it into a sustainable business through hog farming (her idea). He also weighs whether or not it is proper to dance to jazz music. (For more on “Downton Abbey” and its creator, Julian Fellowes, click here.)

Speakeasy caught up with Bonneville to talk about the new season. Excerpts:

Is it unusual in the UK to have a television show written exclusively by one person, as “Downton Abbey” is?

We don’t have the economies of scale that the American industry has, so we don’t have a tradition of having a big team or writers and 13 or 22 episodes a season. It’s usually one man in his attic producing five or six if we’re lucky. Julian’s work rate is amazing, and for him to put his hand to every word of every episode maintaining a quality and a variety and level of surprise for the audience and the cast alike, is quite remarkable. That’s one of the reasons the show feels unique and has found its own niche, is because it is penned by one person—and not just penned by one person. His hand is in every department in a benign god-fatherly way, his attention to the detail of the show, along with our other producers Gareth Neame and Liz Trubridge, they form a triangle of creativity with Julian driving it. But I think it’s that single authorial voice that has benefited each and every one of the episodes.

When you talked to Julian Fellowes about “Downton,” what was it about the idea that captivated you?

The country house estate, the country house itself, particularly in this era, was one of the few environments to place a drama where you can see a cross section of society in one place. The other places were a police station or a hospital or an airport, which would be too transient. But explains why those precincts are so popular, certainly in the dramatic canon of TV. And so, when he was telling me about [“Downton”] “I said I’d love to read it when it’s ready.”

So you get the first five scripts and then each week is a surprise?

No, every February when we all get together again he tends to have two scripts that are ready to shoot and then three sometimes four others. They are in various stages of development. It’s the only time really, that every single actor is in the room to hear the whole story told. Once we start shooting the scripts come in gradually as we progress.

Does he tell you what will happen to your character?

Not really, because he doesn’t know himself. I think even he would admit that when he started writing Season 1 he had no idea it would go beyond that at all. It was a miniseries with high hopes. To think we are going into our fifth, he has to move the goalposts every year in terms of the trajectory of character and story to assess where characters are going, what needs to be pared back. So, beyond those initial scripts, it’s always a delight to find out that one is still alive in the next episode.

The Earl of Grantham experienced a lot of sadness in Season 3—the loss of a daughter in childbirth and a son-in-law in a tragic car accident, as well as the fact that poor Lady Edith was left at the altar. Were you nervous that Season 4 would be too grim in the aftermath of so much tragedy?

Well really, we would have been doing the story of Mary and Matthew a disservice if we didn’t explore the depth of that grief, but—it being TV land—we also need to move on.

Without revealing any spoilers, which might be challenging, what surprised you the most about your character this season?

I think the surprise that I had was the tension between the dinosaur in him and the modernizer in him, the liberal instinct. On the one hand, for me as a 21st Century viewer, I was interested in how out of touch he was with Mary’s grief, or the way to deal with Mary’s grief. He had a Victorian approach of smothering her in cobwebs and his view that she should grieve probably for the rest of her life, or be allowed to come through her grief in her own time and should not engage with the outside world. Clearly this flies in the face of my own instincts as a human being. So there’s that side, his emotional stubbornness or lack of sensitivity, but at the same time he’s a compassionate man. I find the contradictions very human.

I thought his willingness to dance to this newfangled jazz music was impressive.

That’s right. When it comes down to it, he’s the one prepared to go into the future when it comes to managing the estate, having been very reluctant at first. When [a new African-American character] Jack Ross appears, this band leader from a culture and a race that has never been seen at Downton, he might find it terribly shocking but he’s going to have a good dance. So there are contradictions all over the place, but that’s one of the attractions of the show.

Do you ever talk to Julian Fellowes about lines that you don’t like, or offer changes?

Yes, absolutely. To be honest, those conversations have been few and far between because these stories are so solid. He’s the puppet master of 12 to 15 much-loved, established characters and they all pop out of his imagination. I completely trust the artistic triangle of our two producers and Julian. Having said that there have been a couple of times when I didn’t understand this particular path we were going down and needed clarification. I will write a one line email saying “Can you clarify this?” Then there will come a three page explanation of why I am saying it. So he is nothing if not thorough and he can argue a point of view. He’s given birth to these ideas, these stories. There was a line in the season finale when I questioned a particular word—I thought it sounded anachronistic. I said “Can I change it to another word?” And he wrote back, “No! That word was used in an essay in 1888 and I want it in!”

What word?

Dodgy.

Do you think that Downton will ever be able to become a self-sustaining estate?

About Speakeasy

Speakeasy is a blog covering media, entertainment, celebrity and the arts. The publication is produced by Barbara Chai and Jonathan Welsh with contributions from the Wall Street Journal staff and others. Write to us at speakeasy@wsj.com or follow us on Twitter at @WSJSpeakeasy or individually @barbarachai.